Electrical master-slave tap changing system



Oct. 27, 1964 H, E. PINNEY ETAL ELECTRICAL MASTER-SLAVE TAP CHANGING SYSTEM Filed March 9, 1960 2 Sheets-Sheet 1 SOURCE [I Fig].

CIRCULATING CURRENT CONTROL LORD I 5 GEARING [-01 I 'III I REMOTE CONTROL CENTER u rvl-l full llllllll'lllllllll Oct. 27, 1964 H. E. PINNEY ETAL ELECTRICAL MASTERSLAVE TAP CHANGING SYSTEM Filed March 9, 1960 2 Sheets-Sheet 2 Q wuwSsw United States Patent 3,154,734 ELECTRICAL MASTER-SLAVE TAP CHANGWG SYSTEM Harold 1E. Pinney and dohn H. Kuisti, Pittsfield, Mass, assiguors to General Electric Company, a corporation of New York Filed Mar. 9, 196%, Ser. No. 133315 4 Claims. (til. 323-435) This invention relates to electrical systems and more in particular to control circuits for insuring automatic parallel operation of units in a system.

When a plurality of parallel-connected voltage regulating transformers are automatically controlled, one or more of the transformers may sometimes be removed from service to save transformer losses during light load periods. In such a case, it is usually desirable to render the automatic voltage regulating means inactive so as to prevent unnecessary wear on the regulator. The result is that when the non-operating transformers are re-connected to the system with the operating transformers, their voltages may be suiilciently different from that of the operating transformers to cause an excessive circulating current to flow. Furthermore, when sensitive circuit breaking elements are employed, the excessive circulating currents may cause continual tripping of the circuit breakers with the resulting inability to get the non-operating transformers back into the system. Although solutions to this problem have been proposed in the past, the circuits employed were relatively complex and expensive.

It is, therefore, an object of our invention to provide a new and improved electrical system.

Another object of our invention is to provide a control circuit for causing a follower unit to parallel a master unit.

Another object of our invention is to provide an improved control circuit for equalizing the voltage of separate components of an electrical system.

Still another object of our invention is to provide an arrangement for preventing excessive circulating current when one or more non-operating transformers are connected in parallel with other operating transformers.

According to one aspect of our invention, we provide means for adjusting the voltage of a transformer disconnected from a system of transformers connected in parallel between a common power source and a common load before the disconnected transformer is re-connected to the system. The means is characterized by the use of a polarity sensitive relay connected between potentiometers that are associated with the voltage regulating means so that their output voltages vary in a pre-determined manner according to the voltage supplied by the transformer.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing:

FIG. 1 is a schematic diagram of circuits and apparatus illustrating an embodiment of our invention.

FIG. 2 is a schematic diagram of circuits and apparatus illustrating another embodiment of our invention.

Referring now to the drawing and more in particular to FIG. 1, therein is shown a power system comprising two power circuits and 10' supplying a common load 13. Since these circuits and the apparatus associated with them are substantial duplicates of each other, the same reference numerals will be used to describe similar elements in each of the circuits and the elements will be distinguished by prime marks for identifying them with their respective associated circuits.

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The two circuits 10 and 10' are supplied by a common source of power 11 which may be connected to the primary winding of the load tap changing transformer units 12 and 12'. The two circuits are also shown to have a common load 13 which is connected across the secondary windings of the load tap changing transformers by parallel leads. The taps of the respective transformers may be changed by any of the suitable arrangements 14 and 14, and the control of the tap changing mechanisms will be described more in detail in the following paragraphs.

In a control system according to our invention, one of the transformer units will be a master unit and the other units will be follower units whose operation will conform to that of the master unit. For the purposes of illustration, the transformer 12 will be designated the master unit, it being understood that any other transformer could just as readily be the master unit. The tap changer 14 on the master unit may be connected by conventional means comprising gearing 15 to a motor 16 which can run in either direction and thus cause the tap changer 14 to move in either direction. The motor 16 may be run by any convenient power source 23 The motor 16 is connected through suitable gearing 17 to a potentiometer. In the illustrated embodiments, the potentiometer as shown as a variable resistance or rheostat 18, it being understood that other types of potentiometers could also be employed. These elements are arranged in a pre-determined manner so that the output voltage between one end of the potentiometer and its slider 24 is proportional to and varies with the position of the tap changer arm. The follower unit 12' is connected in identically the same manner to a potentiometer or variable resistance 18'. The potentiometers are connected in parallel across any convenient common source of D.-C. voltage 40. The sliders 24 and 24 are connected to each other through any conventional type of polarity sensitive relay 20. The polarity sensitive relay 20 in turn is connected to switches 21 and 21 that will cause a lowering of the respective tap changing mechanisms, and to switches 22 and 22 that will cause a raising of the respective tap changing mechanism. The switches 21, 21', and 22, 22' are respectively connected to the tap changer operating motors 16 and 16' so as to control the direction of rotation of the motors and thus raise or lower the tap changer arms to control the voltage supplied by the transformer.

The operation of the above control system is as follows. Assuming that the follower unit 12' has been taken out of operation by opening the circuit breakers 19', and that the master unit 12 has been in continued operation and its taps have moved to a higher position than that occupied by the taps of the unit 12 at the time it was taken out of operation, then the value of voltage between the slider 2 and one end of potentiometer or resistance 13' will be, for example, greater than that between the same points of the potentiometer or resistance 18; consequently there will be a diiference in voltage between the slider 24' and the slider 24. In this situation D.-C. current will flow across the polarity sensitive relay 2% from potentiometer 18 to potentiometer 18. This will cause the relay 20 to trip the switch 22 and thus cause the motor 16 to rotate in a direction such that it will bring the tap changer 14 and the slider 24 into the identical position with the tap changer 14 and the slider 2 Thus, the output voltages of the otentiometers will be equal, and no current will flow across the relay 20. This will cause the switch 22' to open and the motor 16 to stop. Had the taps on the master unit 12 moved in the opposite direction at the time the follower unit was out of operation, then the voltage between the slider 24' and the beforementioned end of potentiometer 18 would have been less than the voltage across the corresponding points of potentiometer 18,

I 3 thus causing current flow through the polarity sensitive relay 20 in the opposite direction with a subsequent actuation of the relay 20 to close the switch 21 and move the motor 16 and tap changer 14 in the opposite direction.

It will be obvious to one skilled in the art that the potentiometers could be connected so that the voltage between the slider and reference end of potentiometer 18' is less than that between corresponding points of potentiometer 18 when the unit 12 is at a higher tap position. Then the only necessary modification in the circuit would be that the polarity sensitive relay 20 would have to be connected in such a manner that the switch 22' would be closed when the D.-C. current flows from the slider 24 to the slider 24'. Other variations of the manner in which the potentiometers, polarity sensitive relay, and the associated raise and lower switches can be connected to achieve the same result will be apparent to those skilled in the art, and it is not intended to illustrate or describe all of the equivalent variations herein.

In order to designate which unit will be the master unit and which the follower unit, a remote control center 30 may be provided with a master-follower switch 31 having contacts M, F, and M, F. In the illustrated embodiment of FIG. 1, when the switch 31 is moved to the left, the contact F in circuit 10' will be closed and the motor 16 will be connected so as to be actuated by the switches 21' and 22 when the control system operates as described above. In this situation the contact M in circuit 10 will be closed, and master unit 12 will thus not be affected by the paralleling sequence that brings follower unit 12' into the system. Also, in order to change the positionof the taps when the units are in operation and thus control the transformer output voltage, the remote control center 30 may be provided with raise and lower switches 32 and 32'. It will be understood by those skilled in the art that the voltage control switches 32, 32' may be actuated either manually or automatically in response to voltage responsive regulating means of any Well known type. Thus, by closing contact M in circuit 10, the tap position of master unit 12 can be raised or lowered by operation of switch 32, and follower unit I2 will be caused to assume a parallel tap position because the diiference in positions of the sliders of potentiometers l3 and 13' cause the sequence of operations described above. In order to remove a unit from operation when desired, the remote control center may be provided with circuit breakers l9 and 19'. 1

Referring now to FIG. 2, therein is illustrated an embodiment of our invention in which three transformer units 12, I2 and 12" are connected in parallel, it being understood that any greater number of units may be connected in parallel in the identical manner. In FIG. 2 the same numerals .as are employed in FIG. 1 are used to designate the various elements, with the like elements eing designated by the prime and double prime marks. A comparison of the circuits 10, lib and It)" in FIG. 2 will reveal that each individual circuit in FIG. 2 is identical to the others. Each circuit in FIG. 2 is also identical to the circuits in FIG. 1, with the exception of the fact that each circuit in FIG. 2 has its own individual polarity sensitive relay that closes only its own raise and lower switches, and that the polarity sensitive relays in FIG. 2 are Y connected to a common point 60. Obviously, if a greater number of units were in the system, their associated polarity sensitive relays would be connected in a similar manner to the same or a common point, Consequently, if master-follower switch 31 is moved to contact M so that the unit 112 is the master unit, and switches 31' and 31" moved to contacts F and P so that the units 12' and 12 are follower units, it will be apparent that when the taps of any follower unit are at a different position from those of the master unit, the 11-0. current will flow through the polarity sensitive relay of the follower unit and also the polarity sensitive relay 281 of the master unit 12. The direction of D.-C. current flow will be such that it will trip the appropriate raise or lower switch and thus cause the sliders of the otentiometers and the taps of the follower units to move to the same position as those on the master unit, in the same manner as was explained above with regard to FIG. 1. It will be evident from an inspection of FIG. 2 that any unit could be designated the master unit with identically the same relationship existing. That is, the D.-C. current would flow through the polarity sensitive relay of the master unit and, also through the relay of any follower unit that was on a difierent tap position. 7

It will be appreciated by those skilled in the art that the arrangement of FIG. 1 could also employ a separate polarity sensitive relay for each of the circuits I0 and It), with the polarity sensitive relay of each circuit actuating only the raise and lower switches associated with its transformer unit, in the same manner as in the arrangement of FIG. 2. Although this latter arrangement is more expensive, it has the advantage that each of the circuits is identical; thus other identical circuits could be connected into the system, without the necessity of rewiring the original circuits so that each has its own polarity sensitive relay.

It will also be appreciated by those skilled in the art that additional circulating current control systems for minimizing circulating currents fiowing between those units in operation could easily be employed in conjunction with the master-follower system of our invention.

Such a system has been designated schematically as 50 in FIGS. 1 and 2, and could, for example, be a controlled circuit of the type disclosed in US. Patent 2,322,249 to Minneci, which is assigned to the assignee of the present invention.

Although there has been shown and described particular embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein and that our control system could be employed in other combinations without de- 40 parting from the invention. Therefore, it is intended in the appended claims to cover all such changes and modifi-' cations as fall Within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination with a plurality of variable voltage electric transformers each including a movable tap-changing member, separate reversible motor means for moving r each said tap-changing member, voltage control means for actuating said motor means to adjust the associated tap-changing member to a desired position, a plurality of direct current potentiometers connected in parallel circuit relation and having movable sliders each coupled for 5 movement synchronously with one of said tap-changing members, said potentiometers providing across corresponding portions thereof separate signal voltages of like polarity proportional in magnitude to displacement of the associated tap-changing member from a terminal position, a polarity responsive relay having an actuating winding connected between each pair of said movable sliders and oppositely responsive to opposite polarity differences in the magnitude of said signal voltages, switching means g actuated by each said relay and connected to control forward and reverse operation of one said motor means, and a selector switch for disabling the switching means associated with any selected one of said motor means and simultaneously connecting said one selected motor means for actuation by said voltage control means, whereby said one tap-changing member acts as a master voltage controller and all other said tap-changing members follow its operation in synchronous positional relation.

2. An electric system as recited in claim 1 wherein means are provided for selectively connecting two or more of said transformers in parallel circuit relation to a com- References Cited by the Examiner mon alternating current line. UNITED STATES PATENTS 3. An electric system as recited in claim 1 in which said 648 494 5/00 Hewlett 307 51 transformer, motor means and potentiometer S a e a 1 51 9 12 27 ch igt 3()7 51 only two in number, and a single polarity responsive relay 5 2:508:162 5/50 Hel-Wald is connected between the potentiometer sliders. 2 7 9 4 10 5 Erbe 313-29 4. An electric system as recited in claim 1 wherein said 2 913 591 11 59 Smith et 1 303*33 X transformers, motor means and potentiometers are greater 3,060,359 10/62 Schebler 318-29 than two in number, and a polarity responsive relay is connected between each potentiometer slider at a com- 10 LLOYD MCCOLLUM Pllmary Exammer' 111011 point, IVIILTON O. HIRSHFIELD, Examiner. 

1. IN COMBINATION WITH A PLURALITY OF VARIABLE VOLTAGE ELECTRIC TRANSFORMERS EACH INCLUDING A MOVABLE TAP-CHANGING MEMBER, SEPARATE REVERSIBLE MOTOR MEANS FOR MOVING EACH SAID TAP-CHANGING MEMBER, VOLTAGE CONTROL MEANS FOR ACTUATING SAID MOTOR MEANS TO ADJUST THE ASSOCIATED TAP-CHANGING MEMBER TO A DESIRED POSITION, A PLURALITY OF DIRECT CURRENT POTENTIOMETERS CONNECTED IN PARALLEL CIRCUIT RELATION AND HAVING MOVABLE SLIDERS EACH COUPLED FOR MOVEMENT SYNCHRONOUSLY WITH ONE OF SAID TAP-CHANGING MEMBERS, SAID POTENTIOMETERS PROVIDING ACROSS CORRESPONDING PORTIONS THEREOF SEPARATE SIGNAL VOLTAGES OF LIKE POLARITY PROPORTIONAL IN MAGNITUDE TO DISPLACEMENT OF THE ASSOCIATED TAP-CHANGING MEMBER FROM A TERMINAL POSITION, A POLARITY RESPONSIVE RELAY HAVING AN ACTUATING WINDING CONNECTED BETWEEN EACH PAIR OF SAID MOVABLE SLIDERS AND OPPOSITELY RESPONSIVE TO OPPOSITE POLARITY DIFFERENCES IN THE MAGNITUDE OF SAID SIGNAL VOLTAGES, SWITCHING MEANS ACTUATED BY EACH SAID RELAY AND CONNECTED TO CONTROL FORWARD AND REVERSE OPERATION OF ONE SAID MOTOR MEANS, AND A SELECTOR SWITCH FOR DISABLING THE SWITCHING MEANS ASSOCIATED WITH ANY SELECTED ONE OF SAID MOTOR MEANS AND SIMULTANEOUSLY CONNECTING SAID ONE SELECTED MOTOR MEANS FOR ACTUATION BY SAID VOLTAGE CONTROL MEANS, WHERE- 